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United States Patent |
5,224,402
|
Pettersson
|
July 6, 1993
|
Screw and screwdriver therefor
Abstract
A screw includes a socket adapted to receive the tip of a screwdriver. The
socket is tapered and formed by a plurality of sides interconnected by
rounded corners. Each side is configured as a surface of a segment of a
cone having a cone angle of at least three degrees. The screwdriver tip is
configured correspondingly to the screw socket. The screwdriver may be
mounted in a power driven rotary arm and spring-biased, whereby a
tightened screw applies a rearward reaction force to the screwdriver,
causing the tip to be displaced from the screw socket and thereby limit
the torque applied to the screw.
Inventors:
|
Pettersson; Lars T. (Glen Rock, NJ)
|
Assignee:
|
Sandvik Aktiebolag (Sandviken, SE)
|
Appl. No.:
|
577530 |
Filed:
|
September 5, 1990 |
Current U.S. Class: |
81/467; 81/436 |
Intern'l Class: |
B25B 023/14 |
Field of Search: |
81/436,467,58
411/403
|
References Cited
U.S. Patent Documents
2921984 | Dec., 1959 | Ansingh.
| |
4700442 | Oct., 1987 | Lahm | 29/568.
|
4827811 | May., 1989 | Vickers | 81/436.
|
4834597 | May., 1989 | Andersson et al.
| |
Foreign Patent Documents |
2608892 | Sep., 1977 | DE | 411/403.
|
747810 | Jun., 1933 | FR.
| |
113786 | Feb., 1926 | CH | 81/436.
|
753367 | Jul., 1956 | GB.
| |
Primary Examiner: Meislin; D. S.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis
Claims
What is claimed is:
1. Apparatus for rotating screws, comprising:
a power-driven rotary arm rotatable about a longitudinal axis;
a screwdriver mounted to said rotary arm for rotation therewith and being
movable relative thereto along said longitudinal axis, said screwdriver
including a tip adapted to be received in a correspondingly shaped screw
socket, said tip being tapered and formed by a plurality of sides
interconnected by rounded corners, each said side configured as a surface
of a segment of a cone having a cone angle of at least ten degrees; and
torque regulating means for regulating the amount of torque applied to the
screw comprising spring means biasing said screwdriver forwardly and being
yieldable rearwardly in response to said tip being displaced from the
screw socket by a predetermined reaction force applied to said tip by a
tightened screw.
2. Apparatus according to claim 1, wherein there are three said sides.
3. Apparatus according to claim 1, wherein each of said sides is configured
as a surface of a segment of a truncated cone.
4. Apparatus according to claim 1 including means for adjusting a spring
force of said spring means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to screws and to screwdrivers for applying
torque to the screws by manual or mechanical force.
A screwdriver for applying torque to a screw typically comprises a shank
whose free end or tip is configured in complementary fashion to a socket
formed in a head of the screw so as to be capable of mating with, and
transmitting torque to, the screw.
Manual screwdrivers which are commercially available include, at their
tips, drive surfaces which face in the direction of rotation to engage
correspondingly oriented driven surfaces of the screwdriver. For example,
a flat-headed screwdriver possesses radially extending drive surfaces
which face in the direction of rotation; Torx and Phillips screwdrivers
possess longitudinally extending drive surfaces which face in the
direction of rotation. The tips of the Torx and Phillips screwdrivers may
possess a taper, e.g., from 10.degree. to 50.degree., to facilitate entry
of the tip into the screw socket.
Further, there have been proposed so-called tamper-resistant screws which
so termed that because they resist being unscrewed by conventionally
shaped screwdriver tips. For example, as disclosed in German OS 26 08 892,
a screw is provided with a multi-lobed socket each lobe of which is
configured as a segment of a cone having a taper (i.e., cone angle of
approximately 3.degree.). The screwdriver tip has multiple sides
correspondingly curved to mate with the screw socket. In that type of
arrangement, there are no torque-transmitting surfaces facing in the
direction of rotation. Rather, the torque is transmitted from a radially
outwardly facing surface on the screwdriver to a radially inwardly facing
surface in the screw socket. However, the curved sides of the screwdriver
intersect one another to form generally sharp edges. Since, as noted
above, the torque is transmitted between radially facing surfaces, there
may occur a tendency for the screwdriver to be cammed out of the socket
during a turning operation. As that occurs, the sharp edges will tend to
cut the lobes of the screw socket in a manner causing the socket to become
rounded and thus unable to be properly driven by the screwdriver.
It would be desirable to provide a screwdriver/screw arrangement of the
latter type which is easier to make and use and which minimizes any
tendency for the screwdriver tip to cut the sides of the screw socket.
Screwdrivers have also been utilized in automated equipment, as exemplified
by Lahm U.S. Pat. No. 4,700,442. In order to regulate the torque applied
to the screw, the screwdriver includes two shank sections rotatably
interconnected by inclined slide faces. The two shank sections are
yieldably urged together by a spring. When the rotary torque exceeds a
threshold value, the slide faces move axially relative to one another and
terminate the application of torque to the screw. However, such a
mechanism increases the complexity and number of components of the
mechanism.
It would be desirable to provide for automatic torque regulation in
automated equipment without the need for forming the screwdriver in
multiple parts.
SUMMARY OF THE INVENTION
The present invention relates to a screw, a screwdriver, the combination of
a screw and screwdriver, and an apparatus including a power-driven rotary
arm for carrying a screwdriver.
The screw comprises a threaded post and a head disposed at a rear end of
the post. The head has a socket adapted to receive a tip of a screwdriver.
The socket is tapered and formed by a plurality of sides interconnected by
rounded corners. Each of the sides is configured as a surface of a segment
of a cone having a cone angle of at least 3.degree..
A screwdriver according to the invention comprises a shank having a tip
adapted to be received in a correspondingly shaped socket of a screw. The
tip is tapered and is formed by a plurality of sides interconnected by
rounded corners. Each of the sides is configured as a surface of a segment
of a cone having a cone angle of at least 3.degree..
The present invention also involves a machine for rotating screws. The
machine comprises a power driven rotary arm rotatable about a longitudinal
axis. A screwdriver is mounted to the arm for rotation therewith and is
movable relative thereto along the longitudinal axis. The screwdriver
includes a tip adapted to be received in a correspondingly shaped screw
socket. The tip is tapered and formed by a plurality of sides
interconnected by rounded corners. Each of the sides is configured as a
surface of a segment of a cone having a cone angle of at least 10.degree..
A torque regulating mechanism is provided for regulating the amount of
torque applied to the screw. The torque regulating mechanism comprises a
spring biasing the screwdriver forwardly and being yieldable rearwardly in
response to the tip being displaced from the screw socket by a
predetermined reaction force applied to the tip by a tightened screw.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and advantages of the invention will become apparent from the
following detailed description of a preferred embodiment thereof in
connection with the accompanying drawings, in which like numerals
designate like elements, and in which:
FIG. 1 is a longitudinal sectional view through a screw according to the
present invention;
FIG. 2 is a plan view of the screw depicted in FIG. 1;
FIG. 3 is a cross-sectional view taken along the line 3--3 in FIG. 1;
FIG. 4 is a side elevational view of a hand-held screwdriver according to
the present invention;
FIG. 5 is a cross-sectional view taken along the line 5--5 in FIG. 4;
FIG. 6 is a cross-sectional view taken through a screwdriver tip which is
nested within a screw according to the present invention; and
FIG. 7 is a schematic longitudinal sectional view taken through a power
driven rotary arm of a machine carrying a screwdriver according to the
present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
A screw 10 according to the present invention is depicted in FIGS. 1-3, and
a hand-held screwdriver according to the present invention for applying
torque to the screw is depicted in FIGS. 4 and 5.
The screw 10 includes a threaded post 12 which extends axially from an
enlarged head 14. The head includes a central socket 16 for receiving a
tip of the screwdriver. The socket comprises a plurality of curved sides
or lobes 18 interconnected by rounded corners 20. Each side is configured
as a surface of a segment of a truncated cone, with the cone axes of the
various segments being non-coincident. Preferably, the socket has three
sides and three corners, whereby the socket may be considered as being of
tri-lobed shape. A cross-section taken through the head 14 (FIG. 3) shows
that at any given axial position along the socket, each side 18 is
generated by the rotation of a radius R about a point P which is spaced
from the geometric center C of the socket. That point can be spaced from
the center C in a direction toward or away from the respective side 18
being generated. The radii R for all of the sides would have equal lengths
within a given cross-sectional plane.
The socket 16 is tapered from its open end to its floor 22, i.e., each cone
segment which defines one of the sides 18 has a cone angle A. Thus, the
length of the radius R of each side 18 becomes progressively smaller as
the floor 22 is approached. The size of the cone angle A is at least
3.degree., which is large enough to enable the screw head to be
economically manufactured by a cold-forging process. Furthermore, the
entry of the screw driver tip into the socket is facilitated by such a
taper.
The hand-held screwdriver 30 includes a manually grippable handle 32 which
carries a metal shank 34. The shank 34 terminates in a free end or tip 36
which is configured in a complementary fashion relative to the socket 16.
That is, the tip includes a number of sides or lobes 38 interconnected by
rounded corners 40, the shape and number of sides and corners
corresponding to those of the socket. Thus, the sides are shaped as
segments of a truncated cone. Each lobe 38 is tapered to define a cone
angle B which corresponds to the taper A of the socket. The sides 38 are
generated by radii which correspond to those of the socket so that the tip
36 may nest snugly within the socket, as depicted in FIG. 6 which
constitutes a cross-section through the screw head 14 and a screwdriver
tip 36 nested therein.
It will be appreciated that the torque-transmitting sides and corners of
the screwdriver tip and socket face radially outwardly. Thus, all of the
torque is transmitted between radially outwardly facing sides and corners
which are tapered longitudinally toward the longitudinal axis L.
Consequently, upon the application of a torque from the sides and corners
of the tip 36 to the sides and corners of the socket, the sides and
corners of the socket apply to the screwdriver tip a reaction force having
an axially rearwardly directed component which tends to push the
screwdriver out of the socket. The magnitude of that rearward axial force
is a function of the size of the cone angle A, B, i.e., the larger the
angle, the greater the axial force. In the case of a hand-held screwdriver
30, that force can be overcome by the manual application of a sufficiently
large forward axial force to the handle 32.
By making the corners 40 of rounded configuration, the ability of the screw
driver tip to cut the sides of the screw socket is minimized. Thus, there
is less risk that the socket will become rounded to the extent of being
incapable of receiving rotary forces from the screwdriver.
In the case of a machine-driven screwdriver 50 (see FIG. 7) having a tip
36' corresponding in shape to the previously described tip 36, the
imposition of the axially rearward reaction force can be used to advantage
in achieving a limitation of the torque applied to the screw. In fact, the
size of the cone angle is increased, e.g., to at least about 10.degree. to
increase the rearward reaction force. The screwdriver 50 includes a shank
34' mounted within a bore 52 of a rotary arm 54, the arm being
motor-driven within a machine. The shank and bore can be of non-circular
cross-sectional shape to prevent relative rotation between the shank and
arm 54. The shank 34' is linearly movable within the bore 52 and is biased
forwardly by a spring 56. The arm 54 is movable toward a screw 10 which is
mounted in a member 58. The member 58 may comprise a workpiece being
fastened by the screw, or a permanent component of the machine which is
being adjusted in some fashion by rotation of the screw. The spring 56
applies a sufficient bias to the shank 34' to maintain the tip 36' within
the screw socket during the screw rotating step. As the screw becomes
tightened, the resistance to turning increases the axial push-out or
reaction force applied to the shank 34' increases. By selecting a suitable
spring force for the spring 56, the torque at which the spring 56 yields
to enable the tip to exit the screw socket can be preset. As a result, an
automatic limitation of the applied torque is achieved without the need
for slip-type clutches previously employed for that purpose. If desired,
the ability to adjust the spring force can be provided, e.g., by the
provision of an adjusting screw 60 which displaces a plate 62 to change
the compression of the spring 56.
Movement of the tip 36' out of the screw socket does not result in any
appreciable deformation of the socket walls, because the corners of the
screwdriver are rounded rather than being pointed, and thus will not cut
into the socket walls.
In the event that the tip 36' is not angularly aligned relative to the
screw socket when the tip is initially advanced against the screw, the
spring 56 enables the screwdriver to retract. During subsequent rotation
of the screwdriver, the tip becomes angularly aligned with the socket and
snaps into place.
It will be appreciated that the present invention provides a screw and
screwdriver whose socket and tip, respectively, are uniquely shaped to
facilitate manufacture and use. That is, the provision of a socket and tip
having radially outwardly facing force transmitting surfaces tapered by at
least 3.degree. enable the screw and screwdriver to be made easily by cold
forging, and to be axially mated without difficulty. The rounded corners
on the screwdriver tip prevent the tip from cutting into the screw socket.
Furthermore, the unique shape of the screwdriver tip and screwdriver
socket is utilized in combination with a spring to produce a
torque-limiting action in automated equipment.
Although the present invention has been described in connection with a
preferred embodiment thereof, it will be appreciated by those skilled in
the art that additions, modifications, substitutions, and deletions not
specifically described may be made without departing from the spirit and
scope of the invention as defined in the appended claims.
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